Flame-retardant additives and methods of making and using the same are well-known in the prior art. Flame retardant additives are added to many polymers during processing so as to render the finished product made with such polymers resistant to ignition.
One class of flame retardants that is used extensively in industry comprises halogenated polymers of styrenic monomers. An example of a commercially successful product of this class is a brominated polystyrene flame retardant additive sold by the Ferro Corporation of Cleveland, Ohio, under the trademark PYRO-CHEK.RTM. 68PB.
U.S. Pat. No. 4,352,909 which is owned by Ferro Corporation discloses a method for producing a brominated polystyrene flame retardant additive such as PYRO-CHEK 68PB. Additional examples of references that disclose methods for producing brominated styrenic polymers are Naarmann et al., U.S. Pat. No. 4,143,221, Diebel et al., U.S. Pat. No. 4,200,703 and Lindenschmidt et al., U.S. Pat. No. 4,360,455.
Brominated styrenic polymers are utilized to impart flame-retardant properties to a broad range of polymeric resins. Such polymeric resins include, for example, polyamides, polyesters such as PET and PBT, polyolefins and styrenic polymers such as HIPS, ABS, SAN, etc. Unfortunately, the use of commercially available flame retardant additives, such as conventional atactic brominated polystyrene, in high temperature resins such as, syndiotactic polystyrene resin or certain high temperature polyamides is generally not feasible. For example, the use of conventional brominated polystyrene additives in high temperature polymeric resins can lead to a material having unacceptable color and inadequate levels of thermal stability.
Nakano U.S. Pat. No. 5,200,454 talks briefly of adding a halogenated syndiotactic polystyrene to syndiotactic polystyrene polymeric resin. However, Nakano '454 provides absolutely no insight into the physical properties of such additive or how one can produce such an additive.
The commercial trend over the last ten years has been to utilize host polymeric resins displaying increasingly higher working temperatures. The present invention meets the challenges created by this trend by providing a flame-retardant additive that is well suited for use in today's high temperature polymeric resins.